Extruder for the production of foils

ABSTRACT

For adjusting the slit width of an extruder for the production of foils or webs, the extruder body is enclosed in a housing defining a compensation chamber, sealed by an elastic packing which extends around the mouth of the extruder slit, and a constant pressure difference being maintained between the compensation chamber and the distributor chamber of the extruder body.

United States Patent 11 1 1111 3,726,628 Herzhoff et al. 5] Apr. 10,1973 [54] EXTRUDER FOR THE PRODUCTION [56] References Cited OF FOILSUNITED STATES PATENTS [75] Inventors: Peter Herzhoff, Leverkusen; HansGref, Cologne; Wolfgang 3,600,750 1/1971 Stroszynski ..425/376Schweicher, Leverkusen, an f Gap 3,039,143 6/1962 Nicholson ..425 466many 3,122,789 3/1964 Coffee ..425 466 3,528,485 9/1970 Vogel ..l64/343X [73] Assignee: Agfa-Gevaert Aktiengesellschaft,

1 Leverkusen Germany Primary ExaminerJ. Spencer Overholser 22 Filed; Apt2 197 Assistant Examiner'Michael 0. Sutton A l H tz 21 Appl. No.;138,107 omey Como] y & u

ABSTRACT [30] Foreign Application Pmmty Data For adjusting the slitwidth of an extruder for the May 8, 1970 Germany ..P 20 22 415.1production of foils or webs, the extruder body is en- 7 closed in ahousing defining a compensation chamber, sealed by an elastic packingwhich extends around the 425/466 mouth of the extruder slit, and aconstant pressure dif- [51] Int. Cl. ..B29f 3/04 ference beingmaintained between the compensation [58] Fleld of Search ..425/38l, 466,224, chamber and the distributor chamber of the eXtI-uder 425/376, 192,461, 462, 463, 472; 164/343, body 4 Claims, 1 Drawing Figure PATENTEDAPR 1 0191s INVENTORS:

PETER HERZHOFF, HANS GREF, WOLFGANG SCHWEICHER.

EXTRUDER FOR THE PRODUCTION OF FOILS The invention relates to extrudersfor the production of foils, for example photographic films, or for thecoating of supports, for example with photographic emulsons.

The viscous solution to be extruded is fonned into a wide, very thinweb, the thickness of which often has to be controlled to a highstandard of accuracy. The solution is forced from a distributor chamber,which is under super-atmospheric pressure, through a layerforming slit.The slit has to be made very carefully to comply with the standards ofaccuracy required as any deviation from the nominal slit width is shownas thickness errors in the extruded web. The web thickness isapproximately proportional to the third power of the slit width. Sincethe distributor chamber is under internal super-atmospheric pressure,elastic deformations of the cast body and thus of the sensitivelayer-forming or coating-forming slit can occur. The casting units aretherefore generally provided with complicated adjustment mechanisms, forexample, pressure and tension screws, with the aid of which the slit ofthe casting unit is adjusted to the nominal slit width. This operationusually requires considerable care. However, the adjustment only remainscorrect for a quite specific pressure in the distributor chamber. If

this pressure is changed, for example by an alteration in the extrusionspeed or an alteration in the viscosity of the material to be extruded,the adjustment has to be carried out again.

According to the present invention, there is provided an extruder withan adjustable slit width for the production of foils or webs wherein theextruder slit protrudes from a housing enclosing and moveably supportingthe extruder body, the housing defining a closed compensation chambersealed by an elastic packing which extends around the mouth of theextruder slit, a constant pressure difference being maintained betweenthe compensation chamber and the distributor chamber of the extruderbody.

In accordance with one preferred embodiment, this pressure differencehas the value zero. The same pressure then obtains in the compensationchamber and in the distributor chamber of the extruder body. It isobvious that it is not necessary to exactly maintain the 2, equality ofthe pressures, providing they are substantially equal.

The compensation chamber is preferably filled with a pressure medium ofgas or liquid.

In this way, the effect is obtained that the extruder body is always inforce equilibrium, so that deformations are avoided. One constructionexample of the invention is shown in the accompanying drawing and willhereinafter be more fully described.

The casting solution is introduced into the distributor chamber 1 of thecasting body 2, which consists of two component parts of symmetricalform, and is extruded through the slit 3. The casting body is suspendedso to be freely moveable in the jacket or housing 4. Only the mouth ofthe extruder slit 3 projects from the housing. The jacket chamber 5between the casting body 2 and the housingv 4 is filled with a liquid orgas and is sealed by an elastic packing 6 extending around the mouth ofthe slit 3. The pressure of the liquid or gas in the chamber 5 is alwaysmaintained equal to the pressure in the distributor chamber 1.

What we claim is:

1. An extruder for the production of foils or webs comprising anextruder body, a mouth portion on the extruder body, a slit on the mouthportion, a housing enclosing and movably supporting the extruder bodywith the slit disposed to protrude outside of the housing, the housingdefining a closed compensation chamber sealed by an elastic packing sealwhich extends around and is disposed in sealing contact with the mouthportion of the extruder body, and a fluid pressure means in thecompensating chamber for maintaining a fluid pressure in thecompensation chamber substantially equal to the pressure in the extruderbody whereby the dimensions of the slit are maintained substantiallyconstant.

2. An extruder as set forth in claim 1 wherein the fluid pressure meansin the compensation chamber is a gas.

3. An extruder as set forth in claim 1 wherein the {luiddpressure meansin the compensation chamber is a iqui 4. An extruder as set forth inclaim 1 wherein the elastic packing seal comprises an O-ring seal.

1. An extruder for the production of foils or webs comprising anextruder body, a mouth portion on the extruder body, a slit on the mouthportion, a housing enclosing and movably supporting the extruder bodywith the slit disposed to protrude outside of the housing, the housingdefining a closed compensation chamber sealed by an elastic packing sealwhich extends around and is disposed in sealing contact with the mouthportion of the extruder body, and a fluid pressure means in thecompensating chamber for maintaining a fluid pressure in thecompensation chamber substantially equal to the pressure in the extruderbody whereby the dimensions of the slit are maintained substantiallyconstant.
 2. An extruder as set forth in claim 1 wherein the fluidpressure means in the compensation chamber is a gas.
 3. An extruder asset forth in claim 1 wherein the fluid pressure means in thecompensation chamber is a liquid.
 4. An extruder as set forth in claim 1wherein the elastic packing seal comprises an O-ring seal.